It's interesting to me that we're already seeing conditioning as an answer. It seems so very "American."
Ken I think it's all about value, I don't think that's an "American" thing. People are going to leave a club if they no longer see appropriate value. I also don't think constant complaining is a strictly "American" thing.
Clubs are often very expensive in the US and they are able to charge a premium. Reasons I can come up with for the higher prices are prestige, premium golf, networking and often service.
If people think they can get an equivalent experience (prestige, high quality course, conditioning, pace of play, tee time availability, proximity to home, netowrking/friends...) somewhere else for less without a lot of hassle it would be silly to stay. Similarly people may leave if they can get a better experience even if it cost more (ie better value).
I've left clubs because I've moved. I could have continued as a member paying non-resident dues, but the ones I've left didn't provide sufficient value to continue paying any dues. I have paid membership dues for the last 10 years at a course I haven't visited in that time. I do it because it still has value. The value comes in various forms, but primarily future value that I'll hopefully utilize.